Fine particulates can present an explosion hazard due to build-up of electrical charges. Control of static electricity is needed in industrial settings where an uncontrolled electrostatic discharge (ESD) or spark can result in damage. For example, static discharges can bring about the destruction of integrated circuits during some stages of their manufacture. In explosive environments, such as in grain elevators, or in flammable environments, such as on oil drilling rigs, in refineries, and in solvent-based processes, a static discharge can be extremely dangerous and must be prevented in order to safeguard life and property.
Typical ways for controlling static electric charges include external devices on the filter housing and apparatus to carry electrical charges found on the textile material to ground (e.g., grounding straps or wire). Another approach is to apply a coating of metals or of conductive carbon to the outside surface of fibers used in producing organic polymeric textile material. However, if the coating used is not as flexible as the fiber on which it is placed, flexing of the fiber may cause cracks in the coating that may interrupt or destroy the conductive pathway formed by the coating. Still another strategy to drain off static charges is to produce textile materials incorporating conductive fibers into a matrix of nonwoven filtration media.
Conductive media and filter elements are taught in several patents and publications. U.S. Pat. No. 6,099,726 teaches a static dissipating filter cartridge that uses conductive materials. The filters described are pleated filters with a steel mesh supporting a filtration media where the filter media provide particulate efficiency while the steel mesh provides conductivity. U.S. Pat. No. 5,527,569 teaches a conductive filter laminate using a microporous membrane with electrically conductive particles embedded in it. PCT publication WO 01/37970 to Adilaetta et al teaches a porous media for dissipating electrical charges, primarily for use in filtering hydrocarbon liquids.
Methods for manufacturing conductive and/or static dissipative media can vary along with the composition of the media. Specific production methods and compositions for filter media are described in US Publication US 2007/0028767 to Choi and Soper which is herein incorporated by reference.
Improvements for media and filter element designed to control static electrical charges are desired.